Effect of Substituents on the Bond Strength of Air-Stable Dicyanomethyl Radical Thermochromes
作者:Joshua P. Peterson、Margarita R. Geraskina、Rui Zhang、Arthur H. Winter
DOI:10.1021/acs.joc.7b01188
日期:2017.6.16
series of substituted aryl dicyanomethyl radicals were synthesized, and the bonding thermodynamic parameters for self-dimerization were determined from van’t Hoff plots obtained from variable-temperature electron paramagnetic resonance and ultraviolet–visible spectroscopy. At low temperatures, the radicals dimerize, but the colored, air-stable free radicals return upon heating. Heating and cooling
合成了一系列取代的芳基二氰基甲基自由基,并根据从可变温度电子顺磁共振和紫外可见光谱获得的van't Hoff图确定了用于自二聚的键合热力学参数。在低温下,这些自由基会二聚,但是有色的,空气稳定的自由基会在加热后返回。可以重复进行加热和冷却循环(5–95°C),而不会发生自由基降解并且具有明显的热致变色行为。我们发现哈米特之间的线性自由能关系对取代参数和二聚平衡常数,与对在具有俘获性作用之后,给电子的取代基导致键更弱,而吸电子的取代基导致键更强。密度泛函理论研究[B98D / 6-31 + G(d,p)]显示,二聚体更喜欢滑堆积的几何形状,并具有细长的键。